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THIS SNOWPACK SUMMARY EXPIRED ON January 22, 2016 @ 11:00 pmSnowpack Summary published on January 22, 2016 @ 6:00 am

Issued by
Ben Bernall - Kootenai National Forest

Avalanche Character 1: Wind Slab

Wind Slab avalanches release naturally during wind events and can be triggered for up to a week after a wind event. They form in lee and cross-loaded terrain features. Avoid them by sticking to wind sheltered or wind scoured areas.

Today's travels into the Eastern Cabinets revealed the development of some fairly new and extensive cornice formation with wind slabs of varying thickness on the leeward side of ridgelines. Winds at ridgeline were blowing steady at around 10-15 mph with the occasional strong gust. There is abundant fresh snow available for transport which will likely compound this problem in the near future. Ski cuts on small test slopes revealed shooting cracks that traveled up to 40 yards out with very little efforts.

These wind slabs are highly reactive to any human trigger. Be observant and cautious when playing in any terrain near ridgeline locations that are above 30 degrees in steepness. Triggering one of these wind slabs in steep terrain has the potential to be very destructive.

Storm Slab avalanches release naturally during snow storms and can be triggered for a few days after a storm. They often release at or below the trigger point. They exist throughout the terrain. Avoid them by waiting for the storm snow to stabilize.

In the past 48 hours the Kootenai N.F. has recieved an additioanal 7 inches or more across most locations in the Eastern and Western Cabinets and 4" at SNOTEL sites within the Purcell Range. This combined with additional storms dating back to the previous week has created multiple storm slabs within the snowpack. While the most recent storm snow has primarily formed a concern as a wind slab near ridgelines, the two previous storms that have visited us form a more widespread threat. Stability tests showed a weakness 11 inches below the surface between two storm snow interfaces that failed with moderate force and did not propagate. The other layer is much deeper and may be more of a concern as temperatures climb on Friday and Saturday. This layer failed approximately 30 inches below the surface with hard force (ECTP22) and popped out with a clean shear (quality 1). Though we found this layer on multiple aspects at a fairly consistent depth it seemed to be failing on different weak layers. The most notable was the buried surface hoar on the north aspect.

This storm slab will likely become more reactive to human triggers as the temperatures climb and the snow weakens while taking on the additional stress of a heavier snowpack. Caution is advised through this warming period as triggering a slab at this depth would have high consequences.

Loose Wet avalanches occur when water is running through the snowpack, and release at or below the trigger point. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

On our travels out of the Mountains today the temperatures below 5,000' had already begun to warm and extensive "rollers" were observed as well as some fresh point releases on steeper aspects. With the forecasted weather calling for highs in the low to mid 40's on Friday and Saturday this problem will be on the rise and moving up the hill. At higher elevations the deeper layers may become more reactive and even create the opportunity for deeper slabs to release.

Use caution and choose low complexity terrain as tempertures climb. Be careful around small steep terrain features such as gullies at lower elevation that would increase the consequence of a burial.

Snowpack Discussion

David Thompson SAR is offering a free "Intro to Avalanches" course on Friday January 22nd. The class will be from 7-9 PM at the SAR Barn in Libby. The 2nd day will be at the Keeler warming hut on Saturday and will involve hands on beacon practice, snow pit analysis and a partner rescue demonstration. All are welcome to attend.

Today travels took Nate and I into the Eastern Cabinets up to an elevation of 6,200'. The most notable observations were the previously mentioned wind slabs and extensive shooting cracks on leeward slopes below ridgelines. Changes in snow density and reactivity of slabs were quite obvious as we traveled onto wind affected slopes. As we dropped in elevation away from the effects of wind conditions improved dramatically until we dropped into the 5,000' mark. Below this elevation the snow was getting quite heavy and extensive "roller ball" activity was observed.

Weather and CURRENT CONDITIONS

weather summary

Weather forecast for the Kootenai region is showing a dramatic rise in temperatures coming with moisture. Fridays high temperature for valley locations are expected to be in the mid 40s with an 80% chance of precipition. Saturday will also be a warmer day with a high of 39 degrees forecast for valley locations. It looks to be cooling off slightly on Sunday through Tuesday with highs in the mid 30s then back up to the low 40's on Wednesday and Thursday.

Disclaimer

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

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